Traditional polymers, such as partially hydrolyzed polyacrylamide (HPAM), have poor temperature resistance, salt resistance, and shear resistance. Under high-temperature and high-salt conditions of an oil reservoir, the viscosity of a polymer solution drastically decreases due to hydrolysis, thermal degradation, chain curling and the like of HPAM, and therefore the requirements for enhanced oil recovery and acid fracturing of the high-temperature and high-salt oil reservoir cannot be met. For a hydrophobic associated polymer in which a small amount of hydrophobic groups are introduced into molecular chains, the solution of the hydrophobic associated polymer has efficient viscosifying property, excellent salt resistance, and better temperature resistance and shear resistance, and has a favorable application prospect in enhanced oil recovery and acid fracturing of an oil field.
The properties of a solution of a hydrophobic associated polymer depend on the structure and property of a hydrophobic monomer to a certain degree. The differences in the structure and variety of hydrophobic monomers can greatly affect the properties of the polymer. Hydrophobic monomers that have been reported so far include (methyl) acrylate monomer, styrene monomer, (methyl) acrylamide monomer, allyl monomer, and the like. Acrylate-type hydrophobic monomers, which are extremely sensitive to temperature and pH, can easily lead to the decrease of the viscosity of the polymer solution because of the loss of the association effect of the polymer (Huang Xuehong et al., Study on Properties of Water-soluble Hydrophobic Associated Poly (Acrylamide-Hexadecyl Acrylate ). Journal of Functional Polymers, 2002,14(1):90-94). Although the styrene-type hydrophobic monomer has a rigid benzene ring and can effectively improve the temperature resistance and hydrolysis resistance of the polymer, the benzene ring is too close to a molecular main chain, which is not conducive to the copolymerization of the hydrophobic monomer and acrylamide, and also not conducive to improve the viscosifying effect of the polymer solution (Zhong Chuanyong, Characterization and Heat Resistance of AM-STD-NaAMPS Ternary Hydrophobic Associated Copolymer. Polymer Materials Science and Engineering, 2003, 19 (6): 126-130). The allyl type hydrophobic monomer, due to the presence of allyl groups, is not easily copolymerized with main monomer acrylamide, and the prepared hydrophobic associated polymer has a low molecular weight and an unobvious viscosifying effect (Luo Shan et al., Synthesis and Solution Property of Imidazoline-structured Hydrophobic Associated Polymer. Chemical Research and Application, 2015,27(8):1151-1156). The acrylamide-type hydrophobic monomer whose structure is similar to acrylamide is conducive to a polymerization reaction, but there is a shortcoming of poor resistance to hydrolysis. (Geng Tongmou, Viscosity Behavior of Aqueous Solution of Hydrophobic Associated Water Soluble Polymer P(AM/NaAA/DiAC16). Fine Chemicals, 2007, 24(9): 914-918).
Compared with a single-tailed hydrophobic monomer, a double-tail hydrophobic monomer containing a benzene ring and a long-chain alkyl group (Wu Xiaoyan et al. A Surface-active Two-tailed Hydrophobic Associated Acrylamide Copolymer. Guangdong Chemical Industry, 2014, 41(22): 42-44; Jiang Feng et al. Synthesis and characterization of Two-tailed Acrylamide Hydrophobic Associated Copolymers. Journal of Chemical Industry, 2015,66(3):1215-1220) has the following advantages: by the introduction of the benzene ring, the temperature resistance and hydrolysis resistance of the polymer are effectively improved; by the introduction of the long-chain alkyl group, the hydrophobic association effect of the polymer is improved favorably; a main structure of (methyl) acrylamides is adopted to make the hydrophobic monomer easy to polymerize with acrylamide; the two-tailed structure is conductive to improve the hydrolysis resistance and hydrophobic association effect of the hydrophobic monomer. Therefore, the hydrophobic monomer integrates the advantages of various types of hydrophobic monomers, and can more significantly improve the hydrophobic association effect of the polymer, so that the synthesized hydrophobic associated polymer achieves the purposes of temperature resistance and salt resistance.
For a polymer containing polyoxyethylene ether side chains (L'alloret F et al. Aqueous solution behavior of new thermoassociative polymers. Colloid & Polymer Science, 1995, 273(12): 1163-1173; Yang Mingzhu et al. Study on Properties of Novel Thermosensitive Modified Acrylamide Copolymer. Plastics Industry, 2012, 40(4):35-38), a polyoxyethylene ether chain in the molecule and a water molecule form a hydrogen bond. As the temperature of the solution rises, the effect of the hydrogen bond gradually weakens or the hydrogen bond is broken, the hydrophilicity of the polyoxyethylene ether chain decreases, and the hydrophobicity increases, thereby allowing the polymer to exhibit a favorable thermal thickening effect within a higher temperature range, and show higher apparent viscosity in a salt solution.